1. Field of the Invention
This invention relates to a lens structure, particularly for use as a zoom lens, having movable lens frames within a lens barrel and which is so constructed as to prevent any deleterious reflection of light from occurring on that surface of a guide portion with respect to which the movable lens frames are slidable.
2. Description of the Prior Art
Photographic zoom lenses have generally been constructed so that a pair of movable lens groups is disposed and movable axially between a forward lens adapted to be moved only during focusing and a rearward stationary lens, thereby varying the relative position of the movable lenses and accordingly varying the focal length. In lenses of such construction, however, the inner surface of a guide cylinder within which the frames for the pair of movable lens groups are fitted must be provided with a smooth surface finish so as to permit smooth sliding movement of the frames, and this has been incompatible with the desire to provide an anti-reflection treatment such as a light-intercepting coating or similar streaks on the surface of the guide cylinder.
In a zoom lens of long focal length or great zoom ratio which inherently has a wider range of the movement of the zooming lens, particularly when the first zooming lens is at the rearmost position thereof, the light which has passed through the focusing lens and thereafter reflected by the smooth inner surface of the guide cylinder would give rise to serious damage to the image formation.
One known solution for this problem, which will be described in detail hereinafter in conjunction with the accompanying drawings, is to provide partial sliding portions between the lens frame and the inner surface of the guide cylinder, thereby permitting anti-reflection treatment on the other inner surface of the cylinder other than said sliding portions. However, such a construction could not completely eliminate the above described unpreferable reflections, because of the sliding surfaces which are not subject to the anti-reflection treatment.